There is a 'cm_guid' file that is used by the Cloudera Manager (CM) server to know which host belong to it. It appears that this host may have been part of a different CM cluster or the database was recently changed. This keeps users from inadvertently pointing the agent ot another CM instance.

In any case, the solution is to:

1. Archive/remove the /var/lib/cloudera-scm-agent/cm_guid file.

2. Restart the agent:

sudo service cloudera-scm-agent restart

3. Run the Host inspector, from the Hosts page in CM and verisfy that all hosts are functioning. If other hosts fail, they too may be in this state.